In refining crude oil, product streams typically contain a relatively minor amount of sulfur-containing impurities. Thiols, thiophenes, hydrogen sulfide, sulfur-containing heterocyclic organic compounds, and the like are common examples of such sulfur-containing impurities. Such impurities, however, reduce the desirability of a stream for many uses and may make it unacceptable as a feed for a precious metal catalyzed reformer unit. Also, current antipollution standards greatly limit the amount of sulfur that may be present both in hydrocarbon products and in stack gas emissions. For each of these reasons, it is desirable to find a way to reduce the amount of sulfur-containing impurities in a refined hydrocarbon feed.
To reduce the sulfur content of a refined hydrocarbon feed, it is known to contact it with a material containing copper, iron, nickel, zinc, and compounds thereof, especially where these materials are deposited upon an inert support material.
Pertinent art also includes U.S. Pat. No. 4,113,606, which discloses an improved process for removing an impurity such as sulfur from a refined hydrocarbon feed by contacting the feed with a sulfur-removing material under hydrocarbon sulfur-removing conditions. The improved process employs a solid sulfur-removing material having a pore volume of at least 0.15 cc. per cc., of which at least 5 percent is contained in pores having a diameter in the range 0.1 to 15 microns. A satisfactory material is disclosed having a pore volume in the range 0.15 to 0.8 cc. per cc., and higher; a surface area in the range of from about 2 to 700 square meters per gram; and at least 5 percent of the pore volume in pores having a diameter in the range 0.1 to 15 microns. Emphasized in this reference is the critical importance of pore diameter as determined by the mercury porosimetry method. The presence of a relatively high content of large macropores in the range of 0.1 to 15 microns of a sulfur-removing material was asserted to permit the use of an increased liquid hourly space velocity (LHSV) without diffusion limitation problems and without risk of hydrogen sulfide carry-over into the reformer unit.
Additionally, U.S. Pat. No. 4,163,708 discloses a process for removing thiol impurity from hydrocarbon feed by contacting the feed with a sulfur-removing material at a temperature ranging from about 120.degree. to 400.degree. C. The scavenger is disclosed to be a composite having a copper component and an inorganic porous carrier and having a surface area in the range from about 20 and 1000 square meters per gram.
Not disclosed in any of the pertinent references is the unexpected optimal relationship between porosity and both catalyst reactivity and useful life. The essence of the instant invention is that it is not pore diameter, but rather porosity, that is critical to scavenging activity and catalyst life.
It is an object of this invention to overcome diffusion limitations otherwise limiting the effectiveness of sulfur-removing materials while maintaining the useful life and performance of catalysts.
Other objects of this invention will be clear to one of skill in the art based upon this Specification.